Eddies in the Tropical Atlantic Ocean and their seasonal variability

We study mesoscale eddy characteristics in the Tropical Atlantic Ocean, using 23 yearsof daily altimetry sea level anomalies. Eddies are mainly generated in the eastern boundary up-wellings and in the Brazil current region. They have westward propagating speed reaching 20 cms-1 in equatorial area, decreasing with latitudes. They present typical amplitudes of around 1-5 cm.The largest and most energetic eddies are observed in the equatorial region, in particular in theretroflection of the North Brazil Current (NBC). The seasonal cycle of the main eddy characteristicsshows a marked seasonal cycle along the NBC retroflection and along the western part of the NorthEquatorial Countercurrent (NECC). We propose a criterion using altimetry to analyse the mecha-nism responsible for eddy generation. In the NECC, we argue that eddy generation is mainly due tobarotropic instability of mean surface currents whereas other mechanisms must be invoked for theNBC